The CZ method is one of the methods for manufacturing single crystal silicon.
One of unavoidable problems when the single crystal silicon is grown by the CZ method is “dislocation” which occurs at a solid-liquid interface of a seed crystal when the seed crystal comes into contact with a melt. The dislocation is generated by thermal stress induced within the seed crystal when the seed crystal comes into contact with the melt.
To eliminate the dislocation from the crystal, a so-called Dash neck is required to decrease a crystal diameter to 3-4 mm. FIG. 7 shows a state that a Dash's neck portion 21 having a crystal diameter of 3-4 mm is formed to eliminate the dislocation from the crystal.
There are demands for the manufacture of a large-diameter silicon wafer having a diameter of 300 mm or more in these years, and it is required that a large-diameter, heavy single crystal silicon ingot can be pulled up without any problem. When the neck portion is decreased to a diameter of about 3-4 mm by the necking process, the dislocation is eliminated but the diameter is so thin that there is a possibility that it is impossible to manufacture a large-diameter, heavy single crystal silicon ingot without a problem such as falling of the crystal or the like.
(Prior Art 1)
Patent Literature 1 described later describes an invention that uses a silicon seed crystal with boron B added as an impurity at a high concentration and pulls up a large-diameter, heavy single crystal silicon ingot in a dislocation-free state without performing the necking process.
But, a parameter for suppressing the dislocation caused in the seed crystal is not limited to a concentration of impurity (boron B) added to the seed crystal.
Patent Literature 1:
    Japanese Patent Application Laid-Open No 2001-240493